Effect of the composition and thermal annealing on the transformation temperatures of sputtered TiNi shape memory alloy thin films

After sputter-deposited amorphous TiNi films were subjected to heat treatment higher than 600 K, the shape memory alloys (SMAs) showed strong dependence of the transformation temperatures on heat treatment conditions and composition. Unlike Ni-rich films. the transformation temperatures of Ti-rich films are above the ambient temperature and largely depend on annealing temperatures from 600 to 1200 K. But they remain relatively constant on the various annealing temperature domains, 600-740 K. 740-1000 K, 1000 K +. delimited by exothermic peak's originating from the formation of precipitates. The measurements by differential scanning calorimetry. performed on TiNi thin films annealed below 740 K showed transformation temperatures appropriate for medical applications and very small transformation temperature hysteresis of 3 K. resulting in a beneficial effect of SMA cyclic microactuators. Furthermore. using these lower annealing temperatures reduces both thermal and mechanical stresses and makes possible the development of SMA micro-actuators on substrates, that are unstable at elevated temperatures, and on electronic devices. (C) 2001 Elsevier Science B.V. All rights reserved.